关于塔斯基梅毒实验（Tuskegee Syphilis Study）中故意阻止外部治疗的情况，确实存在多份历史文件和报告证实研究人员（主要来自美国公共卫生服务局，USPHS）不仅拒绝提供治疗，还积极干预参与者从外部来源获取帮助，以确保实验能观察梅毒的“自然进程”直至参与者死亡和尸检。以下基于可靠来源的英文原文和证据，逐点说明这些具体内容。我会先用中文总结，然后提供英文原文引用，并标注来源。
1. 与当地医生和医疗机构合作，阻止参与者接受治疗
研究人员说服马肯县（Macon County）的当地医师不要治疗这些参与者，并分发参与者名单，要求医师将求诊者转回USPHS。同时，他们警告阿拉巴马州卫生部门不要为这些测试对象提供治疗，尤其在1940年代引入移动性病治疗单位时。
英文原文证据："During the forty years of the experiment the USPHS had sought on several occasions to ensure that the subjects did not receive treatment from other sources. To this end, Vonderlehr met with groups of local black doctors in 1934, to ask their cooperation in not treating the men. Lists of subjects were distributed to Macon County physicians along with letters requesting them to refer these men back to the USPHS if they sought care. The USPHS warned the Alabama Health Department not to treat the test subjects when they took a mobile VD unit into Tuskegee in the early 1940s."9b7d03
另一来源补充："PHS researchers convinced local physicians in Macon County not to treat the participants, and instead, research was done at the Tuskegee Institute."650ff0
这些干预是为了防止参与者获得青霉素或其他有效治疗，即使青霉素在1940年代已成为标准疗法。
2. 将参与者名单提供给征兵局，阻止二战期间通过军队医疗系统获得治疗
在1941年，二战期间，一些参与者被征兵并在入伍体检中被诊断出梅毒，被命令立即接受抗梅毒治疗。但USPHS向征兵局提供了一份256名参与者的名单，要求排除他们接受治疗，征兵局遵从了这一要求。
英文原文证据："In 1941, the Army drafted several subjects and told them to begin antisyphilitic treatment immediately. The USPHS supplied the draft board with a list of 256 names they desired to have excluded from treatment, and the board complied."6b90a8
这直接证明了研究人员通过官方渠道阻挠外部治疗，以维持实验的“纯净”观察。
3. 当参与者寻求其他医疗帮助时，通过欺骗或干预阻止获取有效药物
研究人员在整个实验期间（1932-1972年）采取极端措施，确保参与者无法从其他来源获得疗法，包括误导他们认为自己已在接受治疗（实际是安慰剂），并在他们求助时干预。报告强调，他们“went to extreme lengths”来阻止任何外部疗法。
英文原文证据："However, they deliberately denied treatment to the men with syphilis and they went to extreme lengths to ensure that they would not receive therapy from any other sources."3eedd0
另一描述："Multiple times throughout the experiment researchers actively worked to ensure that their su
